Patent GB-811533-A (GB)
Title: Improvements in a process for producing high density hardboard
IPC: D21J1/00
Filed: 1956-12-10
Abstract: A high density hardboard is produced by forming a compact mat of lignocellulose particles having a moisture content of 2 to 25 per cent by weight of the dry lignocellulose, passing the mat at room temperature between pressure rolls at a nip pressure of 1,000 to 5,000 pounds per inch so that its density is at least as high as the desired final density of the hardboard, and curing the sheet at a much lower pressure and at an elevated temperature. The lignocellulose may consist of wood particles obtained by steaming chips of pine, hemlock, cedar, or Douglas fir, beech, birch, maple or other wood, milling the steamed chips in a double disc mill, and partially drying the product in a current of air. To the wood particles may be added a phenol-formaldehyde or urea-formaldehyde resin as binder and a molten hydrocarbon wax, rosin, rosin size, or bitumen, as a waterproofing agent.  A mat may be formed by depositing a layer or superposed layers on a moving screen or belt, or the wood particles may be blown on to a screen having a partially evacuated air space therebeneath.  The mat is preferably passed between the pressure rolls at a speed of at least 25 feet per minute.  The dense sheet thus obtained may be cut into lengths and compressed in a flat bed press at a pressure of 25 to 300 pounds per square inch and at a temperature of from 150 DEG  to 250 DEG  C.  The lignocellulose used may alternatively consist of paper, bagasse, straw, or like plant materials.  The hardboard may be formed as a face veneer on plywood. For example the dense sheet formed by compressing a mat of wood particles and a thermosetting binder between rolls at 1,000 to 5,000 pounds per inch is connected by a phenol-formaldehyde adhesive to one of the plies of a sheet of plywood.  The laminate is then compressed at a lower pressure and at an elevated temperature to set the binder and adhesive.ALSO:A high density hardboard is produced by forming a compact mat of lignocellulose particles having a moisture content of 2 to 25 per cent by weight of the dry lignocellulose, passing the mat at room temperature between pressure rolls at a nip pressure of 1,000 to 5,000 pounds per inch so that its density is at least as high as the desired final density of the hardboard, and curing the sheet at a much lower pressure and at an elevated temperature. The lignocellulose may consist of wood particles obtained by steaming chips of pine, hemlock, cedar, or Douglas fir, beech, birch, maple or other wood, milling the steamed chips in a double disc mill, and partially drying the product in a current of air. To the wood particles may be added a phenol-formaldehyde or urea-formaldehyde resin as binder and a molten hydrocarbon wax, rosin, rosin size, or bitumen, as a waterproofing agent.  A mat may be formed by depositing a layer or superposed layers on a moving screen or belt, or the wood particles may be blown on to a screen having a partially evacuated air space therebeneath.  The mat is preferably passed between the pressure rolls at a speed of at least 25 feet per minute.  The dense sheet thus obtained may be cut into lengths and compressed in a flat bed press at a pressure of 25 to 300 pounds per square inch and at a temperature of from 150 DEG  to 250 DEG C.  The lignocellulose used may alternatively consist of paper, bagasse, straw, or like plant materials.  The hardboard may be formed as a face veneer on plywood. For example the dense sheet formed by compressing a mat of wood particles and a thermosetting binder between rolls at 1,000 to 5,000 pounds per inch is connected by a phenol-formaldehyde adhesive to one of the plies of a sheet of plywood.  The laminate is then compressed at a lower pressure and at an elevated temperature to set the binder and adhesive.